Carbon-Based TiN Work Function Tuning for Multi-Vt Devices
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Solution Overview
Problem
As the semiconductor industry advances to smaller process nodes, such as 10 nm and beyond, there is a challenge in fitting the TiN work function tuning layer of the metal gate in FinFET devices without increasing the thickness, which is essential for achieving lower threshold voltage requirements and accommodating multiple threshold voltage (multi-Vt) devices.
Innovation Solution
The use of a carbon-based TiN atomic layer deposition (ALD) process for the metal gate work function tuning layer, which provides a positive shift in work function compared to a chloride-based TiN layer of the same thickness, allowing for multi-Vt devices without increasing the layer thickness, and incorporating a combination of carbon-based and chloride-based TiN layers for effective work-function tuning.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a chloride-based TiN layer is used for work function tuning, then the work function can be adjusted, but the layer thickness must be increased to achieve the desired work function shift, which is not feasible at smaller process nodes
Solution Approach 1:
The patent changes the chemical composition parameter of the TiN layer by incorporating carbon to form carbon-based TiN (TixCNy). This compositional change fundamentally alters the work function characteristics, enabling a positive work function shift without requiring increased layer thickness. The carbon incorporation modifies the electronic structure and bonding characteristics of TiN, directly achieving the desired work function tuning at constant thickness.
Solution Approach 2:
The patent creates a composite material system by combining titanium, nitrogen, and carbon to form carbon-based TiN (TixCNy). This composite approach leverages the beneficial properties of each element: Ti and N provide the base metal gate functionality, while C introduces the positive work function shift. The resulting composite material achieves superior work function tuning compared to conventional chloride-based TiN, resolving the contradiction between work function precision and layer thickness.
2Productivity
If the process node is reduced to 10 nm and below, then device density and performance are improved, but the available space for work function tuning layers is reduced, making it difficult to accommodate the required layer thickness
Solution Approach 1:
The patent changes the fundamental parameter of work function control from thickness-dependent (conventional TiN) to composition-dependent (carbon-based TiN). By incorporating carbon into the TiN lattice, the work function is tuned through chemical composition rather than physical thickness, enabling effective work function adjustment within the severely constrained thickness budget at 10 nm and below process nodes.
Solution Approach 2:
The patent applies local quality modification by incorporating carbon specifically in the TiN work function tuning layer to achieve the desired positive work function shift. This localized compositional change occurs only where needed for work function control, leaving other layers and regions unchanged. The carbon incorporation is confined to the TiN layer, providing precise local tuning without affecting the overall device structure or requiring additional space.
3Adaptability or versatility
If multiple threshold voltage devices are to be fabricated on the same chip, then device versatility is improved, but the complexity of achieving different work functions without varying layer thickness increases
Solution Approach 1:
The patent enables work function differentiation through compositional parameter changes (carbon content in TixCNy) rather than thickness variations. By controlling the carbon incorporation level during deposition, different work functions can be achieved in different regions or devices on the same chip while maintaining uniform layer thickness. This compositional tuning mechanism simplifies the fabrication of multi-Vt devices compared to conventional approaches requiring different thicknesses.
Solution Approach 2:
The carbon-based TiN layer serves multiple functions simultaneously: it provides the base metal gate functionality, acts as a diffusion barrier, and enables work function tuning through compositional control. This multi-functional material allows different work functions to be achieved within a single layer structure, facilitating multi-Vt device fabrication without requiring multiple separate tuning layers or complex stacked structures, thereby reducing overall device complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the fabrication of multi-Vt devices at process nodes of 16 nm, 10 nm, and 7 nm without increasing the thickness of the work function tuning layers, providing a favorable work function tuning close to the p-type band-edge metal gate and acting as a diffusion barrier, effectively targeting multiple threshold voltage devices in the same chip or wafer.
Implementation Method 1
a carbon-based TiN atomic layer deposition (ALD) process
Implementation Method 2
acting as a diffusion barrier
Data Source
AI summary
Methods of fabricating semiconductor devices are provided. The method includes forming a gate dielectric layer over a substrate. The method also includes depositing a first p-type work function tuning layer over the gate dielectric layer using a first atomic layer deposition (ALD) process with an inorganic precursor. The method further includes forming a second p-type work function tuning layer on the first p-type work function tuning layer using a second atomic layer deposition (ALD) process with an organic precursor. In addition, the method includes forming an n-type work function metal layer over the second p-type work function tuning layer.